Flying control for aircraft



Nov. 10, 1953 F. H. ROBERTSON FLYING CONTROL FOR AIRCRAFT 2 SheetsSheet 1 Filed Oct. 12, 1949 Nov. 10, 1953 F. H. ROBERTSON 1 FLYING CONTROL FOR AIRCRAFT Filed Oct. 12, 1949 2 sheets sheet 2 [:IIIIIHHHIIHIIIIHI lllllHHl.

Patented Nov. 10, 1953 FLYING CONTROL FOR AIRCRAFT Frank Henry Robertson, Carisbrooke, Isle of Wight, assignor to Saunders-Roe Limited, Isleof-Wight, England, a British company Application October 12, 1949, Serial No. 120,917

Claims.

.In modern large and/or high speed aircraft, the aerodynamic loads on the control surfaces (i. e. the elevator, rudder, ailerons) are such that the pilot, with his own unaided strength, is often unable to exert sufficient force to move the control surfaces manually or to hold them against the applied loads.

To meet this difficulty, two alternative solutions have been proposed. The first is the use of power operation for the control surfaces. The mechanisms involved are, however, complicated and expensive, and there is always the danger of failure, with the result that duplication of the power units is advisable, as described for example in United States Patent 2,517,680 and in United States application Serial No. 92,794/49. The second is the use of servo tabs. In this system a mechanical connection is provided from the pilots control member not to the control surface itself, but to a tab hinged to the trailing edge of the control surface, the tab being arranged to move in relation to the control surface, on operation of the control member, in the direction opposite to that in which the control surface is to move in relation to the aircraft, with the result that the aerodynamic load on the tab, when displaced, serves to move the control surface to the desired position. Thus, in the case of an elevator, when it is desired to depress the elevator the tab is raised, and when it is desired to raise the elevator the tab is depressed. Where servo tabs are used the control surface must be mass balanced, both to hold it in adjusted position and to prevent flutter, with the result that the weight of the mechanism required to operate the control surface will exceed that involved by the use of a properly designed power control installation with which, if irreversible operators are included, mass balancing is unnecessary.

The invention makes use of the advantageous features of both of the above described systems and provides, in an aircraft, the combination, with a control surface fitted with a servo tab, of a, variable speed power unit mounted on the control surface, so as to constitute a part at least of the mass balance thereof, operatively connected to the servo tab and operable by the pilots control member to displace the servo tab to a position in relation to the control surface determined by the position of the pilots control member, and at a rate corresponding to the rate of movement of the pilots control member.

Power operated flying control systems, in general, can be made lighter than manual flying control systems. Th system according to the invention provides further saving in weight.

Since the power unit only has to move the servotab relatively to the control surface, it may be made considerably smaller and lighter than is possible when the power unit has to develop the greater power required to effect direct displacement of the control surface in relation to the aircraft structure. A further saving in weight results from the fact that the power unit constitutes part, and may in some cases constitute the whole, of the mass balance required for the control surface.

The saving in weight which can be achieved by the invention is illustrated by the following example, which provides an approximate comparison of the relative weights of three forms of mechanism required to operate the control surfaces of a given large aircraft:

Pounds Power control system operating directly on the surfaces as described in United States This example shows that the power control system of United States Patent No. 2,517,680 is considerably lighter than a comparable system embodying mechanical operation of servo tabs, and that the system according to the invention, in which power units, constituting part of the mass balances of the control surfaces, operate the servo tabs, produces a further reduction in weight.

Another advantage of the system according to the invention is greater safety. Having regard to the fact that the control surfaces are not irreversible, as in normal powered controls, other outside agencies may be employed as safety devices to move the control surface in the event of failure of the power system. Moreover, even if no such emergency safety devices are provided, the control surface is free to float to a neutral and relatively safe position under the aerodynamic loads in the event of power failure.

Furthermore, as a safeguard against failure of the power unit, the control surface may b provided with. aplurality of power; unitsathe. tab being .split; into; sections each operatedjby onezof the power units and the power units being operated in synchronism by the pilots control memher, as described in United States application Serial No. 92,794/49. Then, notwithstanding failure of one of the powerunits, thepflotwill be able to maintain sufficientcontrolaoventhe position of the control surface with.;;,the;;aid :ofzthe others.

In the case of large aircraftj thepower "unit will normally be operated from the pilotscontrol member by a master and slave unit, comprising a ,transmitterconnected to the pilots control mem- ...ber.,and.' a remote -receiver located. adjacent the power unit and serving to followfthemovement imparted-to. the transmitter by the .pilots control member. .An appropriate form of. master. and slave-unit is .an ,electricalnnit .ofthe Selsyntype.

. Preferablythe power. unit. is constituted. by a continuously. running '.e1e.ctric.motor,. a variable .delivery hydraulic pumplidrivenby the...electric motor, and a.hydraulic.motondrivenbythe pump and arranged to actuate the tab, thenpi-lots'con- .131101, member. serving .tovary. the delivery of: the

pump and: a. f0l-10W.-.-.up..gear. being provided .for returning the. pump .deliveryto zerolwhenthe tab hasexecutech the desired rnoven'1ent.--v Othenforms .of. variable .speed power-unit may, however, -be' used if desired.

A preferred flying control system according to I the invention will now be described in detail, by way of example, with reference to its application to the control of an elevator; but" it will be understoodthat an exactly similar system maybe used in-conjunction with anyor all of the other control surfaces, i. e. the rudder or ailerons.

-.The preferred system in question is shown in the accompanyingwdrawings; .in which:

a Fig. 1 is a diagrammatic layout ofthef-completesystem insofar as it relates to,thew.eleyator,

. Fig. 2 is a plan view of one of the power units and associated receiver and gearing, and

Fig. 3 is adiagrammatic section through the elevator showingthe power unit and'the mechaianism whereby it actuates the servo tab.

m-to a .shaftina gearbox I I .so. .that-fore and aft movementvofl the. control zcolumn '1 lhwillwrotate ;the shaft. .As fully described in .United; States zapplication. Serial .No.. .92,'794,/.49, -the shaft i fixed -to-the control column in is geared to a shaft l2 FzfOll. operating four Selsyn transmitters l3, so that .the. actuating member ofv .eachetransmitter receives. a. movement .corresponding. -.in magnitude .and...direotion. .to. that. or the control column .I 0. Associated with. the, gearbox .l L. and. as. fully "described in United States application Serial No. '92,'7 9. i/4 9, are .the servomotorl 4 of. an automatic pilot and a feel generator 15.

"The elevator 6 (see also Fig. 3) ,is-freely hinged to a tail plan I! for movement about an axis l8 .and. carries aservo tab .-I9 divided into four :sec- .itions. Each section of ,thesservo tab l9-is operated. by apower unit 211, which is-in turnactuated .bywa 'Selsyn receiver; 21, each -.-receiver; 2 Lbeing electrically connected ,bya .cable. 22 -to..the. associatedLtransmitter .I 3.

Each powerunit comprises-a constant speed electric motor 29 (Fig. 2) which runs continuously to drive a variable delivery hydraulic pump 32;

.15 .;is.-no:delivery from the pump 32 and the hydrau- 110 motor 33 is,,of course, stationary. As soon as the 'control'columri I0 is moved the receiver 2! is .caused to execute a corresponding movement and turns the first sun wheel 36. Since the follow- 20..up...mechanism,. and thus the second. sun-wheel f. .3 l, ..are stationary, theeffect isto' turn the "planet- .carrief 34..and'thus,to' move aleverK-notshown) utolstart delivery in theappropriate directionfrom "the pump. "This causes the hydraulic motor to rstartand to drive, at a speed 'determin'ed'by the rate of movement of thecontrolc'olumn "10-;the associated section i9 of.the servoitabthrough' a reduction gearing Z3, alshaft24 and bevel gearing T25. The section'i9 oftheservotab ishin'ged'to the elevator on an axis26."The Zshaft il-drives causing i the. second 'sune'wheel 3 1 :of the-differential gear to r'otate.."Since"'.the'first sun=wheel "3&

-isnowistationary,;theieffect i agaimtorotatethe 35 planet-carrier;34,...the gearingUoFthe followaup .mechanism being such as'tdm'ake'the rotation vOpposite. to its original' dire'ct'ron. The 'delivery movement of 'the. tab section "I 9 "correspondingto 0 that of-the control column 'io'has'beenproduced,

the deliveryiis stopped'and movement ceases.

"The. power u'nit'iil is mou'ntednon'.ablacks-t 39 ."(Ffigf3)" fiXed'to the elevator "16 'on' the side the elevator. Itth'er'efore constitutes'partflat least; of .the' mass" balancewequired 'for the elevator. .As indicated inchahrdottd'lines inFig.

.3, .whenthe servo tabiS is raisedinrelati'on ,toilthe elevator3l6,"the latter. is depressed iin relation ,tolthe tail plane llifoy'theaerodynamic jforcesuacting onithe. servo tab,.lthe"elevatorias- ,suming. a position determined .by i the displace- =ment .of'- the::servo...tab. from -the -neutral, posin ..tion-.shown in fulLlines. Sim-ilarly if..the .servo tabsissdepressed, the: elevator-will be raisedin relation-to the tail plane to a-position-,-determined tbylthe displacement of the-servo. tab.

What I claim asirnyzinyenti'on-zand;desirerto r--esecure by. Letters-Patent wis:

1;.111 arr aircraft, the" combination of. 9.1 601]- .ztrolasurface, asservo :tab hinged to Ethe itrailing *edgeeofrisaid: .controL surfaceg-a pilots .control -memb er operati-vei on said =servo .tab only, to .the T'6X01US1OI1 of .saidrzcontrol :surface itself, .tolinitiatermovement of.- said: control-"surface; a vari- :able' i speed-3: power unit mounted; on said. control :surface: andwzcon'stitutingy. in' part". at 1east,--a

mass. balance therefor; :an, operative rconnection --between";said power unit: and-said. "servottab a connection bEtWBEIliSaldTDiIOtS control member and saidspower :unit 1501" rendering: said power unit operative; when'everthe pilotscontrol memben-is 5 moved, =tottdisplace' said:servo tab to a sposition'ande at a rate, determined respectively bythe amplitude, and rate of-movementof the pilots control member, and thereby to impart corresponding movement to the control surface. and means for terminating operation of said power unit on arrival of the servo tab at a position in relation to the control surface selected by the movement of the pilots control member.

2. In an aircraft, the combination of a control surface, a servo tab hinged to the trailing edge of said control surface, a pilots control member operative on said servo tab only, to the exclusion of said control surface itself, to initiate movement of said control surface, a variable speed power unit mounted on said control surface and constituting, in part at least, a mass balance therefor, an operative connection between said power unit and said servo tab, a master and slave unit comprising a transmitter connected to said pilots control member and a remote receiver connected to said power unit and serving to follow the movement imparted by the pilots control member to the transmitter, said master and slave unit serving to render said power unit operative, whenever the pilots control member is moved, to displace said servo tab to a position and at a rate determined respectively by the amplitude and rate of movement of the pilots control member, and thereby to impart corresponding movement to the control surface, and means for terminating operation of said power unit on arrival of the servo tab at a position in relation to the control surface selected by the movement of the pilots control member.

3. In an aircraft, the combination of a control surface, a servo tab hinged to the trailing edge of said control surface, a pilots control member operative on said servo tab only, to the exclusion of said control surface itself, to initiate movement of said control surface, a variable speed power unit mounted on said control surface and constituting, in part at least, a mass balance therefor, an operative connection between said power unit and said servo tab, an electrical master and slave unit comprising a transmitter connected to said pilots control memher, a remote receiver connected to said power unit and an electric cable connecting said transmitter and receiver, said receiver being adapted to follow the movement imparted by the pilots control member to the transmitter, and said master and slave unit serving to render said power unit operative, whenever the pilots control member is moved, to displace said servo tab to a position and at a rate determined respectively by the amplitude and rate of movement of the pilot control member, and thereby to impart corresponding movement to the control surface, and means for terminating operation of said power unit on arrival of the servo tab at a position in relation to the control surface selected by the movement of the pilots control member.

4. In an aircraft, a combination as claimed in claim 1, wherein said power unit comprises a constantly running electric motor, a hydraulic pump, having a variable and reversible delivery, driven by the electric motor, a hydraulic motor driven by the hydraulic pump and serving to operate the servo tab, the pump being adjustable by the pilot control member to drive the hydraulic motor in a direction and at a. speed corresponding to the direction and speed of movement of the pilots control member, and a follow-up gear between the output side of the hydraulic motor and the pump for terminating the delivery of the pump when the servo tab has assumed the position selected by the pilots control member.

5. In an aircraft, the combination of a control surface, a plurality of independently movable servo tabs hinged to the trailing edge of said control surface, a pilot control member operative on said servo tabs only, to the exclusion of said control surface itself, to impart movement to said control surface, a plurality of variable speed power units mounted on said control surface and constituting, in part at least, a mass balance therefor, each of said power units being connected to one of said servo tabs, connections between said pilots control member and said power units for rendering said power units operative in synchronism, whenever the pilots control member is moved, to displace said servo tabs to a position and at a rate determined respectively by the amplitude and rate of movement of the pilots control member, and thereby to impart corresponding movement to the control surface, and means for terminating operation of said power units on arrival of the servotabs at a position in relation to the control surface selected by the movement of the pilots control member.

FRANK HENRY ROBERTSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,827,304 Thurston Oct. 13, 1931 2,057,877 Bragunier Oct. 20', 1936 2,325,548 Roos et a1 July 27, 1943 2,340,524 Fischel et a1 Feb. 1, 1944 2,371,388 Glenny Mar. 13, 1945 2,470,968 Aske May 24, 1949 2,517,680 Knowler et a1 Aug. 8, 1950 2,601,962 Douglas July 1, 1952 FOREIGN PATENTS Number Country Date 572,494 Great Britain Oct. 10, 1945 627,858 Great Britain .d Aug. 17, 1949 OTHER REFERENCES Aviation Week, published weekly by Me- Graw-Hill Publishing 00., 99-129 N. Broadway, Albany 1, N. Y.; Sept. 12, 1949; pages 23 to 30 and 33, page 30 relied on. 

